Redeye,
Its some time since I flew an Astro but 9GPH sounds a bit low, but possible. Do you know what speed she was flying at? The best I can get in terms of fuel saving on a really well set up Enstrom is a fuel saving of about 30% from full rich. I should think if you lean a carb 540 to that extent it will get very rough. I have seen 7.5gph in an Enstrom, P1 only at 50mph with minimum weight. 10gph gives me a reasonable cruising speed of 80 and an endurance of 2.5 hours.